Flexible cold finger for cooling samples to cryogenic temperatures



@1.291999 1 R @WRIGHT 3,423,955

FLEXIBLE COLD FI'NGER FOR COOLING SAMPLES T o CRYOGENIC TEMPERATURES Filed June 8, 1966 sheet ofz INVENT OR ORNEYS Jan. 28, 1969 R c. WRIGHT 3,423,955

FLEXIBLE COLD FI-NGER FOR COOLING SAMPLES TO CRYOGENIC TEMPERATURES Filed June 8, 1966 Sheet Z of2 Hauff/50 ATTORNEYS United States Patent O 16 Claims ABSTRACT OF THE DISCLOSURE An elongated flexible cold finger for use in radiation detection systems or the like including a housing at the free end thereof including a platform supported near the front housing window to support and cool a cryogenic element and having an auxiliary preamplifier support. An elongated flexible line couples the housing to a Dewar and includes a thin wall corrugated tube delivering cryogenic fluid from the Dewar to internal channels in the platform. Fluid delivery rate is controlled by a valve the setting of which regulates the escape of coolant from the platform. A bellows tube and protective stainless steel outer braiding surrounds the corrugated tube. In order to keep heat absorption to a minimum, the bellows tube is evacuated and a nonconductive spacer is provided along the length of the corrugated tube to prevent mutual contact between the bellows and tube.

The present invention relates to cryogenic devices and more particularly to an arrangement for cooling various elements, such as samples and detectors, to cryogenic temperatures.

The behavior of materials and devices at very low temperature is of increasing interest to the experimenter and user. Conventional arrangements in Iwhich the sample to be cooled is rigidly attached to a reservoir containing liquid refrigerants present a quite bulky and awkward package which is difficult, unsafe or impossible to orient to a suitable position for the execution of the desired function.

The present invention provides a flexible connection between the zone to be cooled and the refrigerant reservoir connection which permit-s the cooled zone to be oriented and translated to any suitable position and which results in a much less bulky sample container. Temperature variation, refrigerant economy, and ready access to the cooled zone for sample interchange are provided. Also, according to the invention, a second controlled temperature can be maintained in the same package, so that maximum advantage may be taken of the temperature characteristics of certain auxiliary elements to achieve improved stability or usable sensitivity of the complete system.

Other elements which must be operated at low tempera ture and which must be oriented in various positions or altitudes or which must be located in confined spaces may be accommodated by the system. Temperatures down to the boiling point of the liquid refrigerant used can be obtained by varying the flow rate of the refrigerant to the cooled zone. Higher temperatures may be controlled by maintaining a balance between the cooling produced by the regulated flow of the refrigerant and the combined thermal input from environment, experimental, and controlled electrical heaterinputs. Temperature controlled to +l K. has been obseriled in laboratory tests.

Although a great many types of elements can be cooled for various purposes by the present invention, an example of the invention is hereinbelow described with reference to solid state radiation detectors, such as lithium-drifted radiation detectors and the like. Other uses of the inven- 3,423,955 Patented Jan. 28, 1969 ICC tion include, nter alia, cooling any suitable electrical devlce such as masers, optical lasers, parametric amplifiers, optical or infra-red radiation detectors or samples for examination in various spectrometers in which superior performance is achievable at low temperatures.

The development of solid state radiation detectors represents one of the most `significant advances in nuclear detection techniques. By using solid state detectors, electrical response is linear and resolutions better than 3 kev. for C050 (1333 kev.) can be achieved. However, in order to insure optimum performance, detectors such as lithiumdrift germanium and silicon diodes must be cooled to around 77 K. To accomplish this, it is conventional to store a cooling fluid in a Dewar and rigidly mount on the Dewar an evacuated chamber known in the art as a cold finger.

Conventional cold fingers include an elongated barrel 0r can rigidly connect to the Dewar so that the cold finger axis is fixed relative thereto. The detector is positioned at the forward end of the cold finger and an aluminum or beryllium window is provided which maintains the vacuum but is transparent to certain types of radiation. Although solid state detector elements are not inherently directional, the cold fingers house these elements in such a way that only rays incident to the cold finger axis can be efficiently analyzed by the detection system. Thus, in order to reposition the cold finger, the entire Dewar must be moved or translated.

But because of the size, weight and shape of the Dewar and the extremely cold temperature of its contents, the Dewar cannot be easily nor safely moved. Therefore, to take a reading with conventional systems, it is necessary to bring the samples to the DeWar and mount them at the window end of the cold finger. Not only is this requirement inconvenient, but in the case of radioactive materials involved in spills or leaks, it may be dangerous to handle the sample before a reading is taken.

A purpose of the present invention is to make independent the orientation and position of the cold finger relative to the fixed position of the Dewar by providing a flexible line connection having one end coupled to the Dewar and its free end coupled to the cold finger. Thus, although the cold finger remains directional, and coupled to a stationary Dewar, it can be oriented to receive radiation from virtually any direction, and, equally important, it can be moved to the sample instead of requiring the sample to be brought to it.

Therefore, the flexible cold finger of the present invention is extremely versatile. For example, the end of the flexible cold finger can be pushed through reactor shielding to detect spills or leaks which would otherwise be inaccessible to detecting devices. Moreover, with the flexible cold finger, spills or leaks can be quickly and easily analyzed before handling of the sample is required. The present invention can also be used in scatter chambers, for angular correlation studies, and for measurements requiring variable geometries.

It is therefore an object of the present invention to provvide a new and improved elongated flexible cold finger with a cold element at its free end and having its back end coupled to a stationary source of cooling fluid.

Other and further objects of the present invention will become apparent with the following detailed description when taken in view of the appended drawings in which:

FIGURE l is a longitudinal section illustrating the forward part of the cold finger.

FIGURE 2 is a transverse vertical section partially broken away taken along line 2 2 of FIGURE l.

FIGURE 3 is a side elevation of the detector platform and field effect transistor preamplifier.

FIGURE 4 is a transverse vertical section taken along 3 line 4-4 of FIGURE 3 illustrating the heat exchange platform.

FIGURE 5 is a longitudinal vertical section illustrating the back end of the flexible cold finger.

With reference to the drawings in detail, the forward or free end of the flexible cold finger as seen in FIGURE 1 com-prises a cylindrical housing or can 10 preferably made of thin wall aluminum and having a diameter of approximately 2 inches. Can 10 has at opposite ends enlarged threaded flanges 12 and 13. The forward side of flange 12 is provided with a depression or circular slot 14 in which an O-ring seal is seated. A circular apertured cap 16 is threaded to flange 12. It can be seen that cap 16 and the forward end of can 10 define an enlarged opening through which radiation passes. Before threading cap 16 on flange 12, thin window 18 is fitted in place with its periphery over-lapping the O-ring seal 14. An aluminum washer 17 fits on a small shelf at the back of cap 16, and when cap 16 is threaded tight, window 18 is securely clamped between Washer 17 and flange 12 to provide a firm mechanical clamping action capable of withstanding the considerable force generated by the pressure differential across the thin window, and to simultaneously maintain a vacuum-tight seal against the elastomer gasket.

If the material of can is aluminum, it is preferred that capl 16, washer 17, and window 18 also be of aluminum. The aluminum thickness is approximately 0.25- 0.8 millimeter in order to resist deformation when can 10 is evacuated and so that it is transparent to X-ray, particle and gamma radiation. Other types of window material include beryllium or other types of window material having low attenuation for the radiation being observed and capable of withstanding the pressure differential without gas leakage.

A metal `base 20 is threaded to flange 13 of can 10 and is provided with an O-ring seal 22.

A circular heat exchange copper platform 24 is supported coaxially within can 10 lby four stainless steel rods 26 which extend parallel to the axis of can 10 and have their back ends rigidly attached to base 20 and their for- -ward ends soldered to platform 24. A second set of shorter `posts 28 each having their forward ends in intimate thermal contact with the back side of platform 24 receives the threaded end of a retaining screw 30 which releasably mounts a field effect transistor 32 near platform 24 so as to provide a preamplifier stage in the immediate vicinity of the detector.

A small heater coil 31 is wrapped about field effect transistor 32, and when supplied with a small current, raises the temperature thereof so that the optimum parameters exist for preamplication of the signals fed from the detector to transistor 32. If desired, field effect transistor 32 can be removed before using the flexible cold finger by merely removing the screws 30, in which case the detector output is fed directly to electronic circuitry described.

Platform 24 acts as the heat sink for the detector and the field effect transistor 32. The temperature of field effect transistor 32 depends upon the thermal conductivity of the support posts 28, the temperature of the platform 24 and the input to the heater coil 31 plus any thermal input due to operation of the field effect transistor. The thermal conductivity of the support posts may be varied by the selection of the cross-sectional area, length, and material of construction, and one or both of the support posts may be provided with removable sleeves of relatively high thermal conductivity to provide incremental adjustment. In any event, the thermal resistance between transistor 32 and platform 24 should be calculated to a prescribed value which will permit the field effect transistor to be maintained at its optimum temperature with an average heater power input of only a few milliwatts.

A Teflon box 34 having appropriate compartments for electronic circuitry may he provided in the upper rear part of can 10 and near field effect transistor 32. Communicating with the back side of box 34 and extending through base 20 is a metal conduit 36 through which the electrical leads (not shown) pass. Another metal piece 38, held by screws 37 to the outer .part of conduit 36 carries a plurality of pins 40 which are electrically connected to the leads from circuitry in box 34. In order to maintain a pressure-tight seal, an O-ring seal 42 is also provided at the face of conduit 36.

Referring to FIGURES 3 and 4, heat exchange platform 24 can have a drilled axial opening 35 and a small communicating slot 36a formed in the forward face of platform 24. Slot 36a accommodates the wiring for the detector and opening 35 provides a passageway through which the detector output leads connect to field effect transistor 32. A small groove 38a is formed at the back face of platform 24 to seat a temperature detector (not shown) so that the temperature of the platform can be continuously monitored. To enhance the heat exchange action, a pair of concentric circular fluid passageways 40 and 42 are formed in platform 24 along with a connective radial passageway 44. Inner path 40 communicates with an input port 46 and outer path 42 communicates with an output port 48. After the passageways are milled, a copper closure plate 25 is fitted to the `hack of platform 24, thus confining the passageways.

Detector 50 is supported on platform 24 by being integrally formed with a copper plate 52 which has the same diameter as platform 24 and which is held fast to the front face of platform 24 by a high thermal conducting alloy of any suitable and conventional type. Plate 52 may have a center opening aligned with opening 35 in platform 24. Since copper has a low thermal resistance, the heat flow from the detector to the platform occurs rapidly and uniformly. In a preferred embodiment, the side walls and back face of platform 24 and the forward face of plate 52 are gold plated to reduce the thermal emissivity and to prevent oxidation of the copper platform.

A hollow elongated delivery pipe 54 made of, for example, copper or bronze, has its back end extending rearward through base 20 and its forward end within and communicating with the fluid inlet port 46 of platform 24. Another hollow pipe 56 communicates with outlet port 48 which also extends rearward from platform 24 through base 20. Tube 56 acts as a return line for the cooling medium. A stainless steel hollow cylindrical transition piece 58 has its forward end mounted to base 20 and has a back flange 96 coupled to flexible line 60 of the cold finger to be more fully described below. Transition piece 58 acts as a passageway and protective housing for pipes 54 and 56.

The rear of the flexible cold finger is rigidly coupled to the stationary Dewar (see FIGURE 5) and comprises a metal cylindrical housing l62 with a circular flange 64 mounted at the back side thereof and provided with a circular O-ring seal 66. A metal closing plate 68 is releasably screw mounted to flange 66. A stainless steel tube 70 communicates through plate 68 with the inside of housing 62 and serves as a protective sleeve for an S-shaped cooling medium delivery line 86. The inlet end of line 86 extends axially through but is spaced from tube 70 and communicates with the cooling fluid supply line 74 through a compression hex nut arrangement 76.

A second smaller stainless steel sleeve 78 extends through plate 68 and surrounds the outlet end of an S-shaped exhaust line 88. Line 88 feeds an exhaust pipe 82 which vents to the atmosphere through a manually operated pressure control valve 84. Another compression hex nut arrangement 81 provides the suitable transition from line 88 to exhaust pipe 82.y

In order to extend through flexible line 60 the forward ends of lines 86 and 88 converge and terminate just forward of opening 87 at the front face 0f housing 62.

A cooled sorption type getter, which may be of charcoal, carbon, zeolite, or any material which exhibits sorption action for gases when cooled, engages delivery line 86 and functions to absorb residual gases in a manner described below. To releasably heat the gases trapped in getter 92, heating coils 94, in contact therewith, are fed by leads which are electrically connected through a pin feed-through connector 95 mounted to the front wall of housing 62.

A normally closed valve and fitting arrangement 90 communicates through the walls of housing 62 and, with the attachment of proper equipment, serves to evacuate all spaces communicating with housing 62.

According to the invention, the orientation and position of can is made independent from that of the stationary Dewar by virtue of flexible line 60 connected between transition piece 58 and housing -62 and containing flexible parts of the cooling system. The design of line -60 preserves the efliciency of the cooling system, notwithstanding the length thereof.

In one example, line 60' is approximately eight feet long and comprises a thin wall stainless steel bellows 96 which has its back end soldered to the forward wall of housing 62 and its forward end mounted to the rear flange 98 of transition piece 58. A pair of thin wall corrugated copper or bronze flexible tubes 100 and 102 runs the length of line 60 within bellows 96. Tubes 100 and 102 are hollow throughout their length and communicate with delivery lines 86 and 54 and return lines 56 and 88, respectively. For the purpose of spacing tubes 100 and 102 from each other and from the inner surfaces of bellows 96, each of a pair of Teflon helical coils or cords 104 and 106 is wound along the length of each of the tubes 100 and 102. Cords 104 and 106 provide a random point Contact for the support and spacing of tubes 100 and 102 without detracting from the flexible nature of line 60.

To protect the outer surface of bellows 96 from damage and to limit the degree of bending imparted to flexible line 60, strands of braided stainless steel 108 are helically wrapped in crisscross fashion about bellows 96 and have their opposite ends soldered or otherwise held to flange 98 and housing y62. Thus, the degree of flexing `for line 60 is constrained so that the elastic limits of tubes 1001 and 102 are not reached.

As can be seen in FIGURES 1 and 5, the interior of housing l62 communicates through the spaces within bellows 96 with the interior of can 10 so that these spaces can be simultaneously evacuated. It should be understood that cords 104 and 106 do not block this communication nor otherwise interfere with the evacuation.

In operation, with detector 50 mounted on platform 24 all spaces communicating with the interior of housing 62 are evacuated by suitable apparatus connected to valve 90. During this time, getter 92 is heated to drive off previously absorbed gases. Upon reaching a predetermined low vacuum within housing 62, valve 90 is closed and the heating of getter 92 terminated. Valve 84 is opened to reduce the back pressure in the cooling system and to enable the cooling medium, which is stored at positive pressure in the Dewar, to feed through delivery line 86 into the flexible cold finger. Getter 92, being in contact with metal delivery line 86, is cooled and therefore absorbs practically all of the residual gas in the spaces communicating with housing 62. This action further reduces to a very low figure the vacuum within the spaces within the cold finger.

The cryogenic refrigerant can be of any suitable type, for example, liquefied nitrogen, which is at approximately 77 K., liquefied helium, or gases of the same type. Upon feeding through the corrugated tube 100 into delivery line 54, the fluid passes through the inner and outer paths 40 and 42 of the heat exchange platform 24. With the cooling of platform 24, a heat flow takes place from detector 50 and field effect transistor 32 toward platform 24. The warmed cooling fluid exits platform 24 through tube 56 and flows through corrugated pipe 102 through exhaust line 88 and valve 84 to the atmosphere.

Due to the flexible nature of connecting line 60, the window end of can 10 can be pointed in any direction to receive radiation. Thus, if the sample is in the form of a spill on the wall or floor, an analysis can be performed merely by moving can 10 to the sample and pointing the window toward the sample so that the detector 50 receives radiation therefrom, and corresponding electric signals appear at pins 40. If desired, a standard tripod support (not shown) can be used to hold can 10 steady while taking readings. For transport or storage, the cold finger can be packed in a portable insulated carrying case kept Cold by solid carbon dioxide.

Thus, there has been disclosed a versatile elongated flexible cold finger which affords advantages not heretofore realized by existing apparatus. It should be -understood that various modifications can be |made to the herein disclosed example without departing from the spirit and scope of the present invention. For example, the device may be modified by the incorporation of an intermediate flexible radiation shield which may be cooled to an intermediate low temperature by thermal contact with the waste fluid emerging from the cooling lblock. This intermediate shield will block and dissipate the major portion of the radiant thermal energy emitted by the outer vacuum jacket.

What is claimed is:

1. An elongated flexible cold finger for cooling elements to cryogenic temperatures comprising a housing, a heat exchange platform mounted within said housing for supporting an element to be cooled, a reservoir for storing a cooling fluid medium, said reservoir having physical characteristics which during use make it impractical as a portable piece of equipment, an elongated flexible line having its back end coupled to said reservoir and its forward end free, said housing connected to said free end so that said housing can be moved and directed in any desired direction, said line including an elongated flexible tube which receives from said reservoir and delivers to said housing a cooling fluid medium, and first means coupled to the forward end of said tube for directing the fluid medium into and out of the heat exchange platform to cool the same and thus reduce the element temperature to an optimum operating temperature, and second means receiving the fluid medium from said first means and delivering the same to the atmosphere without the medium again contacting the walls of the flexible tube.

2. A flexible cold finger as set forth in claim .1, wherein said flexible line further includes a flexible hollow bellows surrounding said flexible tube, the forward end of said bellows being connected to said housing and the back end of said bellows being coupled to said reservoir, and the outer walls of said flexible line being in direct communication with the inner walls of said bellows.

3. An elongated flexible cold finger for cooling elements to cryogenic temperatures comprising a housing, a heat exchange platform mounted within said housing for supporting an element to be cooled, a reservoir for storing a cooling fluid medium, said reservoir having physical characteristics which during use make it impractical as a portable piece of equipment, an elongated flexible line having its back end coupled to said reservoir and its forward end free, said housing connected to said free end so that said housing can be moved and directed in any desired direction, said line including an elongated flexible tube which receives from said reservoir and delivers to said housing a cooling fluid medium, and means coupled to the forward end of said tube for directing the fluid medium into and out of the heat exchange platform to cool the same and thus reduce the element temperature to an optimum operating temperature, said flexible line further including a flexible hollow bellows surrounding said flexible tube, the forward end of said bellows being connected to said housing and the back end of said bellows being coupled to said reservoir, said line further comprising spacer means Within said bellows to maintain at least portions of said bellows and tube free from mutual engagement.

4. An elongated flexible cold finger for cooling elements to cryogenic temperatures comprising a housing, a heat exchange platform mounted within said housing for supporting an element to be cooled, a reservoir for storing a cooling fluid medium, said reservoir having characteristics which during use make it impractical as a portable piece of equipment, an elongated flexible line having its back end coupled to said reservoir and its forward end free, said housing connected to said free end so that said housingr can be moved and directed in any desired direction, said line including an elongated flexible tube which receives from said reservoir and delivers to said housing a cooling fluid medium, and means coupled to the forward end of said tube for directing the fluid medium into and out of the heat exchange platform to cool the same and thus reduce the element temperature to an optimum operating temperature, said flexible line further including a flexible hollow bellows surrounding said flexible tube, the forward end of said bellows being connected to said housing and the back end of said bellows being coupled to said reservoir, said line further including an outer protective material about said bellows to limit the amount of bending imparted to the line so that the bending of said tube does not exceed its elastic limit.

5. A flexible cold finger as set forth in claim 2 wherein said tube and bellows are corrugated.

6. A flexible cold finger as set forth in claim 3, wherein a second housing is connected to the rear of said bellows and is capable of being releasably fixed to the reservoir, the second housing interior `being in communication with the interior of said first-mentioned housing through the interior of said bello-ws, a delivery line within said second housing having its back end connected so that it receives the cooling fluid from said reservoir and having its front end coupled with the back end of said tube, and said cold finger further comprising means to enable evacuation of the spaces communicating with the interior of said second housing.

7. A flexible cold finger as set forth in claim 6 further comprising a cooled sorption type getter engaging said delivery line and heating means connected to said getter to selectively heat the same.

8. A flexible cold finger as set forth in claim 1 wherein said element is a solid state detector for detecting one of particle emission and electromagnetic radiation.

9. A flexible cold finger as set forth in claim 1 wherein said second means comprises an outlet line means and valve means coupling said outlet line means to the atmosphere, the setting of said valve means being variable to control the rate of cooling fluid delivery to said platform.

10. A flexible cold finger as set forth in claim 6, wherein said line further comprises a second elongated flexible tube within said bellows, said spacer means maintaining at least portions of said second tube, said first-mentioned tube and said bellows free from mutual engagement, the forward end of said second tube connected to the means delivering the cooling fluid to and from the platform to carry the warmed cooling fluid rearward, a fluid outlet line within said second housing having its forward end coupled to the back end of said second tube, and valve means coupling the back end of Said outlet line to the atmosphere, the setting of said valve means being adjustable to vary the delivery rate of the cooling fluid medium.

11. An elongated flexible cold finger for cooling elements to cryogenic temperatures comprising a housing, a heat exchange platform mounted within said housing for supporting an element to be cooled, a reservoir for storo ing a cooling fluid medium, said reservoir having physical characteristics which during use make it impractical as a portable piece of equipment, an elongated flexible line having its back end coupled to said reservoir and its forward end free, said housing connected to said free end so that said housing can be moved and directed in any desired direction, said line including an elongated flexible tube which receives from said reservoir and delivers to said housing a cooling fluid medium, and means coupled to the forward end of said tube for directing the fluid medium into and out of the heat exchange platform to cool the same and thus reduce the element temperature t'o an optimum operating temperature, said platform having means capable of releasably supporting a second element to be cooled to a second higher controlled temperature.

12. A flexible cold finger as set forth in claim 11 wherein said first-mentioned element is a solid state detector for detecting one of particle emission and electromagnetic radiation and said second element is an electrical preamplifier device.

13. An elongated flexible cold finger for cooling elements to cryogenic temperatures comprising a housing, a heat exchange platform mounted within said housing for supporting an element to be cooled, a reservoir for storing a cooling fluid medium, said reservoir having physical characteristics which during use make it impractical as a portable piece of equipment, an elongated flexible line having its back end coupled to said reservoir and its forward end free, said housing connected to said free end so that said housing can be moved and directed in any desired direction, said line including an elongated flexible tube which receives from said reservoir and delivers to said housing a cooling fluid medium, and means coupled to the forward end of said tube for directing the fluid medium into and out of the heat exchange platform to cool the same and thus reduce the element temperature to an optimum operating temperature, said platform comprising at least one passageway formed therein with an inlet port and an outlet port through which the cooling fluid flows, and said ports communicating with said means for delivering cooling fluid to and from said platform.

14. A flexible cold finger as set forth in claim 13 wherein the forward face of said platform includes a plate of low thermal resistance upon which the detector is to be mounted.

15. An elongated flexible cold finger for cooling elements to cryogenic temperatures comprising a housing, a heat exchange platform mounted within said housing for supporting an element to be cooled, a reservoir for storing a cooling fluid medium, said reservoir having physical characteristics which during use make it impractical as a portable piece of equipment, an elongated flexible line having its back end coupled to said reservoir and its forward end free, said housing connected to said free end so that said housing can be moved and directed in any desired direction, said line including an elongated flexible tube which receives from said reservoir and delivers to said housing a cooling fluid medium, and means coupled to the forward end of said tube for directing the fluid medium into and out of the heat exchange platform to cool the same and thus reduce the element temperature to an optimum operating temperature, and said housing includes a forward threaded flange and a cap threaded thereto, a metallic window being releasably clamped between said flange and cap and sealing means contacting the clamped part of said window, said platform being positioned behind, but near said window.

16. An elongated flexible cold finger for use in radiation detection systems and the like comprising a cylindrical housing having a forward flange, a metallic window overlapping said flange and a cap threaded to said flange releasably clamping said window to the housing, said housing having a rear base plate, a heat exchange platform positioned at the forward end within said housing,

elongated metal rods connected to said base plate and supporting said platform by engaging the back face thereof, said platform having an opening to enable passage of the output leads of the detector, a plate having low thermal resistance secured to the forward face of said platform by being soldered thereto with a high thermoconductivity type alloy,` a solid state radiation detector mounted on the front face of said plate, said platform defining a pair of concentric fluid passageways and an interconnecting radial fluid passageway, the innermost passageway having an inlet port and the outermost passageway having an outlet port, a small slot formed in the back face of said platform to receive a temperature detecting device, a pair of metal posts connected rearward from the back face of said platform, a field effect transistor releasably mounted to the yback ends of said posts, a heating coil engaging said field effect transistor to raise the temperature thereof with the passage of current, a box adapted to house electric circuit elements mounted to and within the walls of said housing at a po-sition near said field eflect transistor, an electric lead conduit mounted to said base plate and extending rearward thereof, said conduit communicating with said box, a pin feed-through device connected to said conduit, a cylindrical hollow metal transition piece having high thermal resistance having its forward end connected through said base plate and having a flange connected to the back end thereof, a fluid delivery pipe having its forward end coupled to said inlet port and extending rearward to a position near said transition piece flange and a fluid return pipe coupled to said outlet port extending rearward to a position near said transition piece flange, a reser-voir storing cooling fluid under pressure, said reservoir having physical characteristics which make it impractical to be a portable piece of equipment during use, a second housing having a rear closing plate with connections rigidly connecting said second housing to said reservoir, said second housing having a forward wall defining an opening therethrough, an elongated ilexible connecting line comprising a flexible thin Wall metallic bellows with high thermal resistance having its forward end connected to said transition piece flange and its back end connected to the forward wall of said second housing at the periphery of said opening therein, a pair of elongated flexible thin wall corrugated low thermal resistant tubes positioned within said bellows, one of said tubes connected to said iluid delivery pipe and the other of said tubes connected to said fluid return pipe, each of a pair of helical spacer cords with high thermal resistance wrapped around the length of each of said corrugated tubes so that portions of said tubes and bellows are maintained free from mutual engagement, a protective coating of braided metal strands with high thermal resistance wrapped about the outside of said bellows and having their forward ends connected to said transition piece flange and their rear ends connected to the forward wall of said second housing, a fluid delivery line having its back end connected to receive the cooling fluid from said reservoir, said delivery line extending through said second housing and having its forward end connected to the one of said corrugated tubes connected to said delivery pipe, a cooled sorption type getter engaging a portion of said delivery line within said second housing and an electric heater coupled to said getter for selectively heating the same, said heater including a pin feed-through device mounted on one of the walls of said second housing, and an exhaust line having its forward end connected to the one of said corrugated tubes connected to said fluid return pipe and having its back end extending through said closing plate, a manually operated -valve means connected to the back end of said exhaust line to vent the fluid moving therethrough to the atmosphere, the setting of said valve means controlling the delivery rate of said cooling fluid through said delivery line, additional valve means connected to said second housing and communicating with the interior thereof, and adapted to cooperate with a Vacuum pump, the interior of said second and said first-mentioned housing being in mutual communication through the interior of said bellows and said transition piece, whereby said firstmentioned housing and detector can be moved and oriented in any desired direction relative to the reservoir and said braided coating prevents bending of said pair of corrugated tubes beyond their elastic limit.

References Cited UNITED STATES PATENTS 3,025,680 3/1962 De Brosse et al. 62--514 3,203,628 8/1965 Schoch 62-55 3,289,424 12/ 1966 Shepherd 62-514 LLOYD L. KING, Primary Examiner.

U.S. C1. X.R. 62-45 

